1. Field of the Invention
The present invention relates to a thinner composition, a method of preparing the same and a method of recovering the same More particularly, the present invention relates to a thinner composition for cleaning/washing an object, (e.g. spray nozzle of a linear coating machine) having a photoresist disposed therewith, a method of preparing the same and a method of recovering the same.
2. Description of the Related Art
When manufacturing a display device including a liquid crystal display device (LCD), a lithography technique is typically applied to produce an electric circuit or pixels for displaying color. The lithography process is used for forming minute patterns on a substrate. A substrate on which a photoresist is coated is then exposed to light by means of a mask having a desired pattern, to transfer the circuit pattern of the mask onto the substrate.
The exposed portion or unexposed portion of the coated photoresist is selectively removed during implementation of a developing process depending upon the particular kind of the photoresist being used. As a result, a photoresist pattern corresponding to the desired circuit pattern is obtained.
Generally, to coat the photoresist (PR) uniformly for implementing the photolithography process, a constant amount of PR is placed onto the substrate. The substrate is then rotated by means of a rotational force to spread the photoresist onto the whole surface of the substrate to form a PR layer.
However, when the PR is coated onto the substrate by means of the rotational force, the PR is spread out not only to a portion on which PR patterns are to be formed but also to portions of the substrate in which PR patterns are not meant to be formed, such as an edge portion, a side portion or a backside portion of the substrate (“referred to as extraneous or undesired portions of the substrate”).
If the PR is allowed to remain on the above described extraneous or undesired portions of the substrate, this might induce contamination of the equipment used in formation of the LCD device, thereby also leading to defects in subsequent processing steps in forming the LCD device. Therefore, after coating the PR component, the excess PR on the undesired portions of the substrate need to be removed. Conventional thinner compositions are typically used to remove excess PR formed on undesired portions of a surface or substrate during implementation of a lithography process. For example in one such conventional process, when the PR is coated on the substrate by means of a spin coating method, the thinner composition is sprayed while spinning the substrate to remove the PR around the periphery portion of the substrate.
However, in situations where the substrate has a square shape including a glass substrate, the distance from the center portion of the substrate to each edge portion is not the same. Thus, the removal of the PR components by spraying the thinner composition during the rotation becomes difficult. Accordingly to overcome the above difficulties, a method of dipping a target edge portion of the substrate on which the PR component to be removed is also used.
According to the above described dipping method, the PR is removed from the undesired portions of the substrate via a straight back-and-forth motion of the thinner spraying apparatus along the substrate edge portion. Nevertheless, even this method still has difficulties in connection with larger sized substrates.
Recently, to solve the above-described difficulty for larger-sized substrates, a linear coating method has been used instead of the rotation method for implementing lithography. That is, without moving the substrate, the PR is coated onto the substrate by using a spray nozzle, the size of which corresponds to one edge of the substrate.
The nozzle moves linearly to form a uniform photoresist layer on the whole surface of the substrate. According to this non-rotational, linear coating method, the PR is coated onto a desired portion of the substrate. Without also coating the PR onto any undesired portions of the substrate, such as the edge portion, the side portion or the backside portion of the substrate. Therefore, a subsequent washing of these undesired portions of the substrate is not required.
However, when the PR is sprayed using the non-rotational, linear coating method, the nozzle state should be kept clean. The reason the nozzle should be kept clean is that after spraying the PR through the spray nozzle and onto the substrate, portions of the nozzle such as the end portion and the periphery portion of the nozzle might become contaminated by the PR residue left from a previous spray coating.
The thickness of the PR layer coated on the substrate is generally very thin, at about 1 μm. Accordingly, a contaminated or unclean PR spraying nozzle due to even minute PR contaminants might affect the coating state of subsequent PR coating processes. That is, for example, when spray coating the PR through a nozzle having both a contaminated portion and uncontaminated portion, this results in a coating layer forming on a substrate with a non-uniform thickness, thereby inducing difficulties or defects in subsequent processing steps in forming an LCD device.
Therefore, a thinner composition for maintaining a PR spray nozzle in a clean state is needed. Moreover, as most of the thinner composition is treated as waste after completing the washing/cleaning process at the spray nozzle, a thinner composition which is able to be separated from the waste thinner and recovered for recycling, thereby reducing the manufacturing costs of the display device is also needed.